Magnetic layers having granular exchange tuning layer

ABSTRACT

An apparatus includes a first magnetic layer including a plurality of grains. The first magnetic layer has a first anisotropy value. The apparatus also includes a second magnetic layer including a plurality of grains. The second magnetic layer has a second anisotropy value that is different than the first anisotropy value. The apparatus also includes an exchange tuning layer including a plurality of grains and located between the first and second magnetic layers. The exchange tuning layer has stronger inter-granular exchange coupling than the first and second magnetic layers. The exchange tuning layer has an anisotropy value less than the first and second anisotropy values.

CROSS REFERENCE TO RELATED CASES

This is a continuation of U.S. patent application Ser. No. 12/978,099,filed Dec. 23, 2010, now U.S. Pat. No. 8,460,805, which is herebyincorporated by reference in its entirety.

BACKGROUND

The present disclosure relates generally to the field of layers formagnetic recording media (e.g., hard disks, removable media,magnetoresistive memory, etc.). More particularly, the disclosurerelates to layers for high anisotropy magnetic recording media includingone or more exchange coupled granular layers.

As the grain size of layers in magnetic recording media is decreased inorder to increase the areal density (e.g., to increase the capacity ofthe media without increasing the media size), a threshold known as thesuperparamagnetic limit is reached for a given material and temperature.The superparamagnetic limit is a physical constraint, beyond whichstable data storage is no longer feasible.

Energy assisted magnetic recording is a recording approach where energyis locally provided to layers of a magnetic recording medium to reducethe coercivity of the recording medium and to temporarily reduce themagnetic field of the medium. These effects allow an applied magneticwriting field to more easily direct (e.g., change, hold) themagnetization of the recording medium. Energy assisted magneticrecording can include heat assisted magnetic recording (HAMR) ormicrowave assisted magnetic recording (MAMR). HAMR systems typicallyapply a combination of a magnetic write field gradient and a thermalgradient to the recording medium. MAMR systems typically apply alocalized electrical field at a high frequency (e.g., a microwavefrequency) to layers of the recording medium. HAMR and MAMR allow forthe use of small grain media layers for recording at increased arealdensities by increasing the supermagnetic limit. HAMR also allows forlarger magnetic anisotropy at room temperature to increase thermalstability, because of the highly stable magnetic materials that are used(e.g., FePt alloys).

SUMMARY

One embodiment relates to a system. The system includes a magneticrecording medium. The magnetic recording medium includes a firstgranular magnetic layer and a second granular magnetic layer. The firstmagnetic layer has a first anisotropy value and the second magneticlayer has a second anisotropy value that is different than the firstanisotropy value. The medium also includes a granular exchange tuninglayer located between the first and second magnetic layers. The exchangetuning layer has stronger inter-granular exchange coupling than thefirst and second magnetic layers. The exchange tuning layer has ananisotropy value less than the first and second anisotropy values. Thesystem further includes a write head configured to provide a magneticfield to the magnetic recording medium. The magnetic field changes orholds the binary value of one or more grains of at least one of thefirst and second magnetic layers. The system further includes at leastone of a heat source and a microwave source configured to provide energyfor energy assisted magnetic recording to the magnetic recording medium.

Another embodiment relates to an apparatus. The medium includes a firstmagnetic layer including a plurality of grains. The first magnetic layerhas a first anisotropy value. The apparatus also includes a secondmagnetic layer including a plurality of grains. The second magneticlayer has a second anisotropy value that is different than the firstanisotropy value. The apparatus also includes an exchange tuning layerincluding a plurality of grains and located between the first and secondmagnetic layers. The exchange tuning layer has stronger inter-granularexchange coupling than the first and second magnetic layers. Theexchange tuning layer has an anisotropy value less than the first andsecond anisotropy values.

Another embodiment relates to an apparatus having multiple layers foruse with a magnetic recording medium. The apparatus includes a firstgranular magnetic layer having a first anisotropy value and a secondgranular magnetic layer having a second anisotropy value that isdifferent than the first anisotropy value. The apparatus also includes agranular exchange tuning layer located between the first and secondmagnetic layers. The exchange tuning layer has stronger inter-granularexchange coupling than the first and second magnetic layers. Theexchange tuning layer has an anisotropy value less than the first andsecond anisotropy values.

Another embodiment relates to an apparatus. The apparatus includes afirst granular magnetic layer having a first anisotropy value, a secondgranular magnetic layer having a second anisotropy value that isdifferent than the first anisotropy value, and a third granular magneticlayer having a third anisotropy value. The apparatus also includes afirst granular exchange tuning layer located between the first andsecond magnetic layers. The first exchange tuning layer has strongerinter-granular exchange coupling than the first and second magneticlayers. The first exchange tuning layer has an anisotropy value lessthan the first and second anisotropy values. The apparatus also includesa second granular exchange tuning layer located between the second andthird magnetic layers. The second exchange tuning layer has strongerinter-granular exchange coupling than the second and third magneticlayers. The second exchange tuning layer has an anisotropy value lessthan the second and third anisotropy values.

Alternative embodiments relate to other features and combinations offeatures as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overhead view of a portion of a disk drive storage systemthat can include a recording medium, according to an embodiment.

FIG. 2 is a schematic illustration of a heat assisted magnetic recordinghead and recording medium, according to an embodiment.

FIG. 3 is a schematic sectional view of magnetic layers of a recordingmedium, according to some embodiments.

FIG. 4 is a schematic sectional view of magnetic layers of a recordingmedium, according to other embodiments.

FIGS. 5 and 6 are schematic sectional views of recording media forheat-assisted magnetic recording, according to two embodiments.

FIGS. 7 and 8 are schematic sectional views of recording media formicrowave-assisted magnetic recording, according to two embodiments.

DETAILED DESCRIPTION

Referring generally to the figures, high anisotropy perpendicularrecording media are shown to include an exchange coupled granularstructure. The media switching field distribution may be reduced by thegranular structure without a significant penalty to the thermal gradientof the media. The coupling efficiency may also be greatly enhanced bythe granular structure, enabling energy assisted magnetic recordingtechnology. The granular structure described herein can be used forultra high density energy assisted magnetic recording such as for HAMRand MAMR. The granular structure may enable a higher areal density dueto an increase of switching field distribution, an increased SNR, and abetter response to the assist energy. In some embodiments, the sequenceof placement of a plasmonic heat sink (PUL) and soft under layer (SUL)may increase the coupling efficiency (CE) and the performance of themagnetic write field of the recording media. A HAMR structure may alsoassist in maintaining a high thermal gradient in the recording layer dueto the disclosed granular structure. Compared to some existing magneticrecording media, each layer of the granular structure may have ananisotropy value (H_(k)) that is higher than the self demagnetization(M_(s)) of the layer. In some embodiments, H_(k) may be greater than4πM_(s).

Referring to FIG. 1, a data storage device or disk drive 10 that canutilize a recording medium is shown, according to an embodiment. Diskdrive 10 includes a housing 12 (illustrated with the upper portionremoved and the lower portion visible) sized and configured to containthe various components of the disk drive. Disk drive 10 includes aspindle motor 14 for rotating at least one magnetic storage medium 16.Disk drive 10 also includes at least one arm 18. Each arm 18 includes afirst end 20 with a recording head or slider 22 and a second end 24.Second end 24 may be pivotally mounted on a shaft by a bearing 26. Diskdrive 10 further includes an actuator motor 28 located at second end 24for pivoting arm 18 to position the recording head 22 over apredetermined sector or track 27 of medium 16. Actuator motor 28 may beregulated by digital or analog electronics or by a controller.

In a MAMR system, an electric current arc at a high frequency (e.g., amicrowave frequency) may be directed onto a surface of data storagemedium 16 to facilitate switching of the magnetization of the area. Insome embodiments, MAMR recording heads include one or more electrodesconfigured to provide a electrical current arc to localized portions ofstorage medium 16. In other embodiments, other types of MAMR recordingheads may be used.

In a HAMR system, an electromagnetic wave of, for example, visible,infrared or ultraviolet light may be directed onto a surface of datastorage medium 16 to raise the temperature of a localized area of medium16 to facilitate switching of the magnetization of the area. In someembodiments, HAMR recording heads include a thin film waveguide on aslider to guide light to storage medium 16 for localized heating ofstorage medium 16. A grating coupler may be used to provide light to thewaveguide. In other embodiments, other types of HAMR recording heads maybe used.

While FIG. 1 illustrates a disk drive, in other embodiments, otherstorage devices may be used that include a transducer, a magneticstorage medium, and an actuator for causing relative movement betweenthe transducer and the magnetic storage medium.

Referring to FIG. 2, a schematic side view of a HAMR recording head 22and magnetic recording medium 16 is shown, according to an embodiment.Although an embodiment is illustrated and described for a HAMR system,in other embodiments, similar elements may be used in conjunction withMAMR systems. Head 22 may include a write section comprising a mainwrite pole 30 and a return or opposing pole 32. Write pole 30 and returnpole 32 are magnetically coupled by a yoke or pedestal 35. In otherembodiments, head 22 may include write pole 30 and not include returnpole 32 or yoke 35. Head 22 also includes a magnetization coil 33 thatsurrounds yoke 35 for energizing head 22. Head 22 may also include aread portion that may be any suitable read head.

Recording medium 16 may be positioned adjacent to or under recordinghead 22. Relative movement and/or rotation of at least one of head 22and medium 16 is indicated by arrow 62, however in other embodiments,relative movement may be in the opposite direction. Medium 16 is shownto include a substrate 38, a heat sink layer 40, a seed layer 41, one ormore magnetic recording layers 42, and a protective layer 43. Magneticfield H produced by current in coil 33 may be used to control thedirection of magnetization of bits or grains 44 in the recording layerof medium 16. For example, magnetic field H may change or hold themagnetization or binary value of each bit 44.

Recording head 22 also includes a structure 50 for heating magneticrecording medium 16 proximate to the location where write pole 30applies the magnetic write field H to recording medium 16. For example,structure 50 may be a planar optical waveguide or another structuresuitable for heating medium 16. Structure 50 conducts energy from asource 52 of electromagnetic radiation, which may be for example,ultraviolet, infrared, or visible light. Source 52 may be, for example,a laser diode, or other suitable laser light source for directing alight beam 54 towards structure 50. Any suitable technique for couplingor providing light beam 54 to structure 50 may be used in varyingexample systems. For example, light source 52 may operate in associationwith an optical fiber and external optics for collimating light beam 54from the optical fiber toward a diffraction grating on structure 50. Inother embodiments, a laser may be mounted on structure 50 and light beam54 may be directly provided to structure 50 without the use of externaloptical configurations. Once light beam 54 is provided to structure 50,the light propagates through structure 50 toward a truncated end 56 ofstructure 50 that is formed adjacent the air-bearing surface (ABS) ofrecording head 22. Light 58 exits the end of the waveguide and heats aportion 60 of medium 16 as medium 16 moves relative to recording head 22(e.g., as shown by arrow 62).

While a specific example of HAMR is illustrated, according to otherembodiments, MAMR techniques may be used instead of HAMR techniques. Forexample, structure 50 may be replaced by a structure (e.g., anelectrode) configured to provide a current arc at a high frequency torecording medium 16. In such an embodiment, light source 52 may replacea power source configured to provide high frequency current to theelectrode. In other examples, other MAMR techniques may be used inconjunction with head 22 and medium 16.

Referring to FIGS. 3-4, various example magnetic layer structures forperpendicular media are shown. Different layers of FIGS. 3-4 may be madeof similar or different materials and may have similar or differentanisotropies. For example, the thinner layers are exchange tuning orbreak layers having a plurality of grains (“granular exchange tuninglayers”). The thicker layers may be magnetic layers having a pluralityof grains (“granular magnetic layers”). The granular exchange tuninglayers have larger exchange coupling and lower anisotropy than thegranular magnetic layers. In various embodiments, even the loweranisotropy exchange coupling layers may have an anisotropy (H_(k))higher than 6 kOe (4πM_(s)). In the illustrations of FIGS. 3-4, thesubstrate, SUL, seed layer, and interlayer are not shown. Rather, forclarity, only the magnetic layers and exchange coupling or exchangetuning layers are shown. It should be appreciated that suitablesubstrates, SULs, seed layers, or interlayers may be a part of one ormore of the embodiments described herein. In some embodiments, each ofthe magnetic layers may record different information. In otherembodiments, each of the magnetic layers may record the sameinformation. That is, the magnetization configuration may be correlatedbetween the grains in different layers. Such a correlation may result inincreased data integrity and/or increased SNR.

Referring specifically to FIG. 3, a dual layer granular structure 300 isillustrated, according to some embodiments. Structure 300 includes afirst granular magnetic layer 302 and a second granular magnetic layer304. First and second granular magnetic layers 302 and 304 are connectedby a granular exchange tuning layer 306. The anisotropy of each ofmagnetic layers 302 and 304 may be greater than the anisotropy ofexchange tuning layer 306.

The anisotropy of layers 302 and 304 may be approximately equal or maybe different. Likewise, the inter-granular exchange coupling of layers302 and 304 may be approximately equal or may be different. Theinter-granular exchange coupling within each magnetic layer 302 and 304may be relatively small with respect to or weaker than the exchangecoupling of exchange tuning layer 306. Exchange-tuning layer 306 may beconfigured to couple grains of the magnetic layers.

When constructing an exchange tuning layer 306, the strength of theexchange coupling performed by exchange tuning layer 306 may be adjustedby varying the thickness of the layer. In some embodiments, exchangetuning layer 306 may be made of ferromagnetic materials. In theembodiments of FIG. 3, each magnetic layer 302 and 304 has highanisotropy. Magnetic layers 302 and 304 may be made of FePt materialswith each layer having different doping amounts or materials. The FePtmaterials may be doped with a non-magnetic or magnetic material at thegrain boundaries or in the grain cores, such as a C, BN, TiOx, or SiOxmaterial or a Cu, Ag, Ni, or Co material. In other examples, layers 302and 304 may be made of other ferromagnetic materials and/or doped withother non-magnetic materials. Magnetic layers 302 and 304 may also beadjusted by varying the thickness. Such adjustment affects signalamplitude for read or playback operations. In some embodiments, thethickness of one or more of layers 302 and 304 may be relatively low inorder to increase signal amplitude.

Referring specifically to FIG. 4, a three layer granular structure 400is illustrated, according to an embodiment. Structure 400 includes afirst granular magnetic layer 402, a second granular magnetic layer 404,and a third granular magnetic layer 406. First and second magneticlayers 402 and 404 are connected by a granular exchange tuning layer408. Second and third magnetic layers 404 and 406 are connected by agranular exchange tuning layer 410. The anisotropy of each of magneticlayers 402, 404, and 406 may be greater than the anisotropy of exchangetuning layers 408 and 410.

The inter-granular exchange coupling within each magnetic layer 402,404, and 406 may be relatively small with respect to or weaker thanexchange tuning layers 408 and 410. Exchange-tuning layers 408 and 410are configured to couple grains of the magnetic layers. Whenconstructing an exchange tuning layer 408 or 410, the strength of theexchange coupling in exchange tuning layers 408 and 410 may be adjustedby varying the thickness of the layer.

In the embodiments of FIG. 4, each magnetic layer 402, 404, and 406 mayhave high anisotropy. In some embodiments, exchange tuning layers 408and 410 may be made of ferromagnetic materials. For example, magneticlayers 402, 404, and 406 may be made of FePt materials with each layerhaving different doping amounts or materials. The FePt materials may bedoped with a non-magnetic or magnetic material at the grain boundariesor in the grain cores, such as a C, BN, TiOx, or SiOx material or a Cu,Ag, Ni, or Co material. In other examples, layers 402, 404, and 406 maybe made of other ferromagnetic materials and/or doped with othernon-magnetic materials. Magnetic layers 402, 404, and 406 may also beadjusted by varying the thickness. Such adjustment affects signalamplitude for read or playback operations. In some embodiments, thethickness of one or more of layers 402, 404, and 406 may be relativelylow in order to increase signal amplitude.

In one embodiment, first and third magnetic layers 402 and 406 haveanisotropy values that are similar or equal. Second magnetic layer 404has anisotropy that may be different than the anisotropy of first andthird layers 402 and 406, but that may still be greater than theanisotropy of exchange tuning layers 408 and 410.

In another embodiment, magnetic layer 402 has lower anisotropy thanmagnetic layers 404 and 406 and has higher or stronger inter-granularexchange coupling than magnetic layers 404 and 406. In an alternativeembodiment, magnetic layer 406 has lower anisotropy than magnetic layers402 and 404 and has higher or stronger inter-granular exchange couplingthan magnetic layers 402 and 404. In another alternative embodiment,magnetic layer 404 has lower anisotropy than magnetic layers 402 and 406and has higher or stronger inter-granular exchange coupling thanmagnetic layers 402 and 406. In each embodiment, the lower anisotropymagnetic layer may still have a higher anisotropy and weaker exchangecoupling than exchange tuning layers 408 and 410. In such an embodiment,the other two magnetic layers each have high anisotropy and weakexchange coupling. However, the specific anisotropy and exchangecoupling of the layers may be different or may be approximately equal.For example, each of magnetic layers 402, 404, and 406 may havedifferent anisotropy and exchange coupling. Within each layer, thespecific grains may be decoupled with the adjacent layer to a greater orlesser degree. Exchange tuning layers 408 and 410 may be varied in orderto achieve an optimal SNR. In some embodiments, one of magnetic layers402, 404, and 406 may be a continuous layer rather than a granularlayer.

A micromagnetic simulation of the magnetization-applied magnetic fieldloop (M-H loop) was completed to compare usage of structures 300 and 400to other magnetic media. The anisotropy distribution of each layer maybe about the same as compare to other magnetic media. However, theresults show that the switching field distribution may be reduced whenat least two granular magnetic layers are exchange coupled together andthe exchange tuning layer has an anisotropy value less than the magneticlayers, but exchange coupling greater than that of the magnetic layers.

Referring now to FIGS. 5 and 6, structures 300 and 400 are shown inmedia structures 500 and 600 that may be suitable for use in a HAMRsystem according to various embodiments. The magnetic and exchangetuning layers of structures 300 and 400 can have anisotropy and exchangecoupling levels as described above with respect to FIGS. 3 and 4. Theanisotropy of each of the granular magnetic layers may be greater thanthe anisotropy of the exchange tuning layer.

Referring specifically to FIG. 5, media structure 500 is shown toinclude the layers of structure 300 as well as a seed layer 502 formagnetic layer 304, a plasmonic heat sink (PUL) 504, a seed layer 506for PUL 504, a first soft under layer (SUL) 508, an Ru layer 510, asecond SUL 512, and a seed layer 514 for SUL 512.

Referring specifically to FIG. 6, media structure 600 includes thelayers of three magnetic layer structure 400 as well as seed layer 502for magnetic layer 404, PUL 504, seed layer 506 for PUL 504, first SUL508, Ru layer 510, second SUL 512, and seed layer 514 for SUL 512. It isnoted that FIGS. 5 and 6 are illustrations and that the overcoat,lubricant, and other layers are not shown. Only the magnetic and opticalfunctioning layers for the HAMR system are shown.

The anisotropy of each magnetic layer can be different to make up agradient H_(k) structure. Each of seed layers 502, 506, and 512, PUL504, SULs 508 and 512, and Ru layer 510 may be any layer appropriate foruse in a HAMR system. In some embodiments, the materials and thicknessof each layer may be appropriately selected based on the properties ofthe layers within structures 300 or 400. For example, Ru layer 510 mayalternatively be an RuO₂ layer, a Ti layer, a Pt layer, etc. In anotherexample, PUL 504 may have a thickness of between about 4 nm and 150 nm,between about 4 and 40 nm, etc. The thickness of PUL 504 may be muchsmaller than the total thickness of SUL layers 508 and 512.

A micromagnetic simulation of the write field from the write pole of theHAMR system, with and without an SUL, was performed by the applicants.For HAMR, the write pole size may be as large as about 300 nm. Theresults of the micromagnetic simulation showed that use of an SULenhances the strength of the total write field by about 80%. For a largewrite pole, the SUL can be further away from the media and the totalwrite field can be still increased as compare to an embodiment withoutan SUL. SULs 508 and 512 may include ferromagnetic materials orsuperparamagnetic materials. For example, SUL 508 or SUL 512 may includeat least one of a CoFe, CoNiFe, CoFeX, CoFeXY, NiFeX, and NiFeXYmaterial, where X and Y are metallic or non-metallic doping materials ofless than about 20% concentration by weight.

A simulation of the field intensity due to usage of PUL 504 in contrastto usage of a non-plasmonic heat sink (e.g., a Si heat sink) wasperformed by the applicants. Usage of PUL 504 was shown in thesimulation to lead to an enhancement of the coupling efficiency (CE).PUL 504 may include materials with good plasmonic properties, such asmetal (e.g., Cu, Ag, etc.) and metallic alloys. It is noted that invarious embodiments, a dedicated thermal barrier layer may be omitted.

Referring now to FIGS. 7 and 8, structures 300 and 400 are shown inmedia structures 700 and 800 that may be suitable for use in a MAMRsystem according to various embodiments. The magnetic and exchangetuning layers of structures 300 and 400 can have anisotropy and exchangecoupling levels as described above with respect to FIGS. 3 and 4. Theanisotropy of each of the granular magnetic layers may be greater thanthe anisotropy of the exchange tuning layer.

Referring specifically to FIG. 7, media structure 700 includes thelayers of structure 300 as well as a seed layer 702 for magnetic layer304, a first SUL 704, an Ru layer 706, a second SUL 708, and a seedlayer 710 for SUL 708. Referring specifically to FIG. 8, media structure800 includes the layers of three magnetic layer structure 400 as well asseed layer 702 for magnetic layer 404, first SUL 704, Ru layer 706,second SUL 708, and seed layer 710 for SUL 708. It is noted that FIGS. 5and 6 are illustrations and that the overcoat, lubricant, and otherlayers are not shown. Rather, for clarity, only the magnetic and opticalfunctioning layers for the HAMR system are shown.

The anisotropy of each magnetic layer can be different to make up agradient H_(k) structure. The top magnetic layer (302 or 402) can have alower anisotropy (e.g., H_(k)>4πM_(s)) than the exchange tuning layer,but still have a much lower anisotropy than the anisotropy of second andthird magnetic layers. Each of seed layers 702 and 710, SULs 704 and708, and Ru layer 706 may be any layer appropriate for use in a MAMRsystem. In some embodiments, the materials and thickness of each layermay be appropriately selected based on the properties of the layerswithin structures 300 or 400. For example, Ru layer 510 mayalternatively be an RuO2 layer, a Ti layer, a Pt layer, etc. SULs 704and 708 may include ferromagnetic materials or superparamagneticmaterials. For example, SUL 704 or SUL 708 may include at least one of aCoFe, CoNiFe, CoFeX, CoFeXY, NiFeX, and NiFeXY material, where X and Yare metallic or non-metallic doping materials of less than about 20%concentration by weight.

A simulation of the SNR penalty for each percentage of anisotropydistribution increase in perpendicular media was performed by theapplicants. The results show that as the write transition widthapproaches the grain size limit, the final SNR depends on the anisotropydistribution. The SNR increases as the anisotropy distribution may bereduced. Additional penalty may be observed if the medium switchingfield (anisotropy) distribution may be large. The resolution wasincreased by enhancing thermal anisotropy in the recording layer byusing a granular layer structure (e.g., structure 300 or 400) instead ofusing continuous layers coupled to each other or a continuous layercoupled to a single granular layer.

FIGS. 5-8 specifically show the use of multiple SULs (e.g., SULs 508,512 and SULs 704, 708) with a layer of Ru (e.g., Ru layers 510 and 706).In other embodiments, the Ru layer (e.g., Ru layer 510, Ru layer 706)and corresponding SUL (e.g., SUL 512, SUL 708) may be omitted. In suchembodiments, the media structure may include a single SUL (e.g., SUL508, SUL 704) and no Ru layer. The single SUL (e.g., SUL 508, SUL 704)may include ferromagnetic materials or superparamagnetic materials. Forexample, the SUL may include at least one of a CoFe, CoNiFe, CoFeX,CoFeXY, NiFeX, and NiFeXY material, where X and Y are metallic ornon-metallic doping materials of less than about 20% concentration byweight.

The construction and arrangement of the components as shown in thevarious embodiments is illustrative. Although only a few embodimentshave been described in detail in this disclosure, those skilled in theart who review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in dimensions, structures,shapes and proportions of the various elements, mounting arrangements,use of materials, orientations, etc.) without materially departing fromthe teachings of the subject matter recited in the claims. For example,elements shown as integrally formed may be constructed of multiple partsor elements, the position of elements may be reversed or otherwisevaried, and the nature or number of discrete elements or positions maybe altered or varied. The order or sequence of any process or method maybe varied or re-sequenced according to alternative embodiments. Othersubstitutions, modifications, changes and omissions may be made in thedesign, operating conditions and arrangement of the various embodimentswithout departing from the scope of the appended claims.

What is claimed is:
 1. An apparatus, comprising: a first magnetic layercomprising a plurality of grains having grain boundaries and a graincore, the first magnetic layer having a first anisotropy value (H_(k));a second magnetic layer comprising a plurality of grains having grainboundaries and a grain core, the second magnetic layer having a secondanisotropy value (H_(k)) that is different than the first anisotropyvalue (H_(k)); a third magnetic layer comprising a plurality of grainshaving grain boundaries and a grain core, the third magnetic layerhaving a third anisotropy value (H_(k)) such that the second anisotropyvalue (H_(k)) less than the first anisotropy value (H_(k)) and the thirdanisotropy value (H_(k)); the first magnetic layer, the second magneticlayer, or both the first and second magnetic layers comprising dopedferromagnetic materials; an exchange tuning layer comprising a pluralityof grains and located between the first and second magnetic layers, theexchange tuning layer having stronger inter-granular exchange couplingthan the first and second magnetic layers, the exchange tuning layershaving an anisotropy value (H_(k)) less than the first anisotropy value(H_(k)) and the second anisotropy value (H_(k)); and a heat sink layer.2. An apparatus according to claim 1, wherein the heat sink layercomprises a plasmonic material.
 3. An apparatus according to claim 1,wherein the heat sink layer comprises metal or metallic alloys.
 4. Anapparatus according to claim 1, wherein the doped ferromagneticmaterials comprise FePt.
 5. An apparatus according to claim 4, whereinthe FePt is doped with a nonmagnetic or magnetic material at the grainboundaries or grain core.
 6. An apparatus according to claim 4, whereinthe nonmagnetic or magnetic material is selected from C, Cu, Ag, Ni, orCo.
 7. An apparatus according to claim 4, wherein the FePt is doped withC, BN, or SiO_(x) materials.
 8. An apparatus according to claim 1,wherein the third magnetic layer comprises doped ferromagneticmaterials.
 9. An apparatus according to claim 1, further comprising atleast one of a seed layer and a soft under layer.
 10. An apparatusaccording to claim 1, further comprising a second exchange tuning layercomprising a plurality of grains and located between the second andthird magnetic layers.
 11. A system, comprising: a magnetic recordingmedium comprising: a first magnetic layer comprising a plurality ofgrains and having a first anisotropy value (H_(k)); a second magneticlayer comprising a plurality of grains and having a second anisotropyvalue (H_(k)); a third magnetic layer comprising a plurality of grainsand having a third anisotropy value (H_(k)) such that the secondanisotropy value (H_(k)) is less than the first anisotropy value (H_(k))and the third anisotropy value (H_(k)); an exchange tuning layercomprising a plurality of grains and located between the first andsecond magnetic layers, the exchange tuning layer having strongerinter-granular exchange coupling than the first and second magneticlayers, the exchange tuning layer having an anisotropy value (H_(k))less than the first anisotropy value (H_(k)) and the second anisotropyvalue (H_(k)); and a heat sink layer; and a write head configured toprovide a magnetic field to the magnetic recording medium, the magneticfield changing or holding the binary value of one or more grains of atleast one of the first and second magnetic layers, the write headcomprising one or more electrodes configured to provide an electricalcurrent to localized portions of the magnetic recording medium.
 12. Asystem according to claim 11, wherein the heat sink layer comprises aplasmonic material.
 13. A system according to claim 11, wherein theelectrical current alternates at microwave frequencies.
 14. A systemaccording to claim 11, wherein the electrical current facilitatesswitching of the magnetization in the localized portion of the magneticrecording medium.
 15. A system, comprising: a magnetic recording mediumcomprising: a first magnetic layer comprising a plurality of grains andhaving a first anisotropy value (H_(k)); a second magnetic layercomprising a plurality of grains and having a second anisotropy value(H_(k)); a third magnetic layer comprising a plurality of grains andhaving a third anisotropy value (H_(k)) such that the second anisotropyvalue (H_(k)) is less than the first anisotropy value (H_(k)) and thethird anisotropy value (H_(k)); an exchange tuning layer comprising aplurality of grains and located between the first and second magneticlayers, the exchange tuning layer having stronger inter-granularexchange coupling than the first and second magnetic layers, theexchange tuning layer having an anisotropy value (H_(k)) less than thefirst anisotropy value (H_(k)) and the second anisotropy value (H_(k));and a heat sink layer; and a write head configured to provide a magneticfield to the magnetic recording medium, the magnetic field changing orholding the binary value of one or more grains of at least one of thefirst and second magnetic layers, the write head comprising a thin filmwaveguide on a slider.
 16. A system according to claim 15, wherein theheat sink layer comprises a plasmonic material.
 17. A system accordingto claim 15, wherein the thin film waveguide guides an electromagneticwave through the slider for localized heating of the medium.
 18. Asystem according to claim 17, wherein the electromagnetic wave comprisesvisible, infrared, or ultraviolet light.
 19. A system according to claim15, further comprising a light source, wherein the thin film waveguideis optically coupled to the light source.
 20. A system according toclaim 15, wherein the write head comprises a grating coupler configuredto provide light to the thin film waveguide.